There has been a demand for lowering a power supply voltage of a system LSI typified by a central processing unit (CPU) and a baseband IC for saving power consumption. On the other hand, lowering of a power supply voltage of a system used heretofore, or a system for processing analog signals has not been advanced in order to maintain compatibility with a conventional system or the like. As a result, when signals are transmitted between circuits of different power supply voltages, it is necessary to shift the level of the signals. As a level shifting device for different power supply voltages, there is a system for shifting a voltage from ±5 to ±3.3 V, for example. In addition, with reduction in a CPU drive voltage, systems for shifting a voltage from ±5 to ±2.5 V, and systems for shifting a voltage from ±3.3 to ±2.5 V are more widely used.
As a system for level shifting, there is a buffer-type level shifting circuit configured of a NAND circuit, a NOR circuit, an inverter, a level shifter circuit and the like. Such a circuit requires directional signals (DIR) for regulating directions of signals, and this increases the number of pins of a connecting terminal, and complicates the circuit. This results in increase in the chip size and price of a circuit.
On the other hand, there is a bus switch with level shifting using a switching effect produced by changing the gate voltage of a transistor, and such a bus switch can be fabricated with a simple circuit configuration. However, it is not easy to control the voltage of an output terminal with high accuracy. For example, variations in a gate threshold voltage results in variations in the voltage of the output terminal.
There is a conventional level shifting semiconductor device for switching the gate voltage of a MOS transistor serving as a switch between a first power supply voltage and a second power supply voltage in response to the voltage of an input terminal.